The present invention relates to hydrometallurgy. More particularly, it relates to the extraction of gallium metal values from aqueous solutions by solvent extraction techniques employing certain N-organohydroxamic acids as extractants. Further, it relates to gallium complexes of such N-organohydroxamic acids and organic solutions thereof.
Solvent extraction hydrometallurgy is employed in industrial operations to recover valuable metals. The key to implementing this technology has been the availability of suitable metal extractants. Metal extractants, hereinafter extractants, are organic soluble compounds that form organic soluble complexes with metals which allow the transfer of the metal values from an aqueous solution to an organic phase containing the extractant in contact with the aqueous solution, i.e., extraction, which can be represented generally as follows:
M.sub.aq +E.fwdarw.ME: (1) PA1 M.sub.aq =metal in aqueous phase: (A) PA1 E=extractant in organic phase: (B) PA1 ME=metal complex in organic phase: (B) PA1 ME+SS.fwdarw.MSS+E: (2) PA1 SS=aqueous stripping solution phase: (C) PA1 MSS=metal in stripping solution phase: (C)
Unwanted nonmetallic and, depending upon the extractant and conditions employed, metallic impurities are left behind in the aqueous phase (A) which is discarded, further processed, or recycled. The metal in the organic phase (B) is then recovered by an aqueous stripping solution phase (C) as follows:
The method by which stripping is done depends upon the nature of the extractant and the metal involved. By the stripping process (2) the extractant is regenerated and recycled repeatedly in the extraction process. The metal, now concentrated and purified in the aqueous stripping solution phase (C) can be recovered by conventional methods.
Such solvent extraction processes from recovering metal values are known. See, for example, Kirk-Othmer, Encyclopedia of Chemical Technology, Third Edition, Vol. 6 pp 850-851, Vol. 9 pp. 713-714. U.S. Pat. No. 3,224,873 issued Dec. 21, 1965 to R. R. Swanson discloses a solvent extraction process employing certain oxime extractants for the recovery of copper. U.S. Pat. No. 3,276,863 issued Oct. 4, 1966 to J. L. Drobnick et al discloses the separation of nickel and cobalt values using certain oxime extractants. U.S. Pat. No. 3,821,351 issued June 28, 1974 to M. F. Lucid discloses certain N-substituted hydroxamic acids useful as extractants for the recovery of copper, molybdenum, uranium, iron and vanadium. U.S. Pat. No. 3,971,843 issued July 27, 1976 to J. Helgorsky et al discloses a solvent extraction process employing certain substituted hydroxyquinolines for the recovery of gallium from aqueous alkaline solutions.
Xiang et al in Acta Metallurgica Sinica 18 (2), 221, (1982) describe the use of a certain undefined fatty hydroxamic acid for the recovery of gallium from aqueous acid solutions.
Iwaya, Japanese Patent No. SHO60(1985) 245736, Appl. No. Sho. 59(1984)-101504, published Dec. 5, 1985, discloses a method of recovering gallium, using hydroxamic acids, described as having --C(O)NHOH groups, from high-basicity aqueous sodium aluminate solutions.
Gallium is a highly valued metal and aqueous solutions containing gallium metal values are obtained from various sources such as zinc production process streams, alumina production process streams and from acid extraction of the flue dust residues from elemental phosphorus production--the so-called "treater dust".
Depending on the source of the gallium solution, various other metal ions may be present in varying amounts, usually in large excess with respect to the gallium (III) ion. These other ions might include aluminum (III), zinc (II), iron (II), and iron (III). A commercial extractant has to exhibit selectivity in extracting gallium (III) in the presence of these other metallic ions. Furthermore, once the gallium (III) has been extracted into an organic solution from the mixture of ions in aqueous solution, it should then be easily extractable, in concentrated form, into another aqueous solution, the so-called stripping solution. In addition, traces of other metallic impurities in the organic solution must be easily removed, i.e., they must not form irreversible complexes with the extracting agent. If such complexes are formed, then the extracting agent in a commercial process will be deactivated and rapidly rendered useless.